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| United States Patent |
5,155,073
|
|
Elvin
|
October 13, 1992
|
Demetallization of hydrocarbon conversion catalysts
Abstract
A demetallization process for catalysts used for chemical conversion of
hydrocarbons, the catalysts containing at least vanadium as a metal
poison, wherein the poisoned catalyst is contacted in a sulfiding zone
with a sulfiding agent and a hydrocarbon having a minimum boiling point of
about 300.degree. F., the hydrocarbon being at least partially vaporizable
at the temperature in the sulfiding zone.
| Inventors:
|
Elvin; Frank J. (Houston, TX)
|
| Assignee:
|
Coastal Catalyst Technology, Inc. (Houston, TX)
|
| Appl. No.:
|
690501 |
| Filed:
|
April 24, 1991 |
| Current U.S. Class: |
502/31; 208/52CT; 208/113; 208/120.01; 208/120.1; 208/120.25; 502/30; 502/32; 502/35; 502/50; 502/516 |
| Intern'l Class: |
B01J 038/56; B01J 038/42; B01J 029/38; C10G 011/05 |
| Field of Search: |
502/34,35,50,31,516,30
208/52 CT
|
References Cited
U.S. Patent Documents
| 4243550 | Jan., 1981 | Burk et al. | 502/27.
|
| 4432864 | Feb., 1984 | Myers et al. | 208/120.
|
| 4541923 | Sep., 1985 | Lomas et al. | 208/113.
|
| 4828684 | May., 1989 | Elvin | 502/516.
|
| 4986896 | Jan., 1991 | Avidan et al. | 502/34.
|
| 5021377 | Jun., 1991 | Maholland et al. | 208/120.
|
Primary Examiner: Konopka; Paul E.
Attorney, Agent or Firm: Browning, Bushman, Anderson & Brookhart
Claims
What is claimed is:
1. In a process for treating a catalyst which has been removed from a
process used for the chemical conversion of hydrocarbons and containing at
least vanadium as a metal poison, and wherein said metal poison containing
catalyst is contacted with at least one sulfiding agent in a sulfiding
zone at an elevated temperature to convert at least a portion of said
vanadium to a vanadium sulfur containing compound and form a sulfided
catalyst, the improvement comprising:
introducing at least one hydrocarbon into said sulfiding zone together with
said sulfiding agent, said hydrocarbon having a minimum boiling point of
about 300.degree. F. and being at least partially vaporizable at the
temperature in said sulfiding zone, said hydrocarbon being introduced into
said sulfider in an amount effective to enhance subsequent vanadium
removal from said catalyst, removing said sulfided catalyst from said
sulfiding zone, chlorinating said sulfided catalyst and removing vanadium
therefrom prior to returning said catalyst to said chemical conversion
process.
2. The process of claim 1 wherein said hydrocarbon is added in an amount of
at least about 0.3 percent by weight based on the weight of the catalyst
being treated.
3. The process of claim 2 wherein said hydrocarbon is added in an amount of
at least about 0.3 to about 5 percent by weight based on the weight of the
catalyst being treated.
4. The process of claim 1 wherein a mixture of hydrocarbons is introduced
into said sulfiding zone, said mixture of hydrocarbons having a boiling
range of from about 330.degree. to about 1000.degree. F.
5. The process of claim 1 wherein a mixture of hydrocarbons is introduced
into said sulfiding zone.
6. The process of claim 5 wherein said mixture of hydrocarbons is selected
from the class consisting of kerosine, diesel oil, gas oil, crude oil, and
mixtures thereof.
7. The process of claim 6 wherein said mixture of hydrocarbons comprises
diesel oil.
8. The process of claim 1 wherein said sulfiding is carried out at a
temperature of from about 500.degree. F. to about 1650.degree. F.
9. The process of claim 1 wherein said sulfiding agent comprises hydrogen
sulfide.
10. The process of claim 1 wherein said catalyst comprises a synthetic
zeolite capable of promoting hydrocarbon cracking.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the removal of metal poisons
from a hydrocarbon conversion catalyst which has been contaminated with
one or more poisoning metals by use in a high temperature catalytic
conversion of hydrocarbon feedstocks to more valuable, lower boiling
products. More particularly, the present invention relates to an improved
process of reducing the vanadium content of such catalysts. The invention
may be used as part of an overall metals-removal process employing a
plurality of processing steps to remove a significant amount of one or
more of nickel, vanadium and iron contained in the poisoned catalyst.
2. Description of the Background
Catalytically promoted methods for the chemical conversion of hydrocarbons
include cracking, hydrocracking, reforming, hydrodenitrogenation,
hydrodesulfurization, etc. Such reactions generally are performed at
elevated temperatures, for example about 300.degree. to 1200.degree. F.,
more often 600.degree. to 1000.degree. F. Feedstocks to these processes
comprise normally liquid and solid hydrocarbons which, at the temperature
of the conversion reaction, are generally in the fluid, i.e., liquid or
vapor state, and the products of the conversion usually are more valuable,
lower boiling materials.
In particular, cracking of hydrocarbon feedstocks to produce hydrocarbons
of preferred octane rating boiling in the gasoline range is widely
practiced and uses a variety of solid inorganic oxide catalysts to give
end products of fairly uniform composition. Cracking is ordinarily
effected to produce gasoline as the most valuable product and is generally
conducted at temperatures of about 750.degree. to 1100.degree. F.,
preferably about 850.degree. to 950.degree. F., at pressures up to about
2000.degree. psig. and without substantial addition of free hydrogen to
the system. In cracking, the feedstock is usually a petroleum hydrocarbon
fraction such as straight run or recycle gas oils or other normally liquid
hydrocarbons boiling above the gasoline range. Recently, low severity
cracking conditions have been employed for heavily contaminated feedstocks
such as crude or reduce crude where the conversion is not made directly to
the most valuable, lower boiling products, i.e. gasoline boiling range
products, but to intermediate type hydrocarbon conversion products which
may be later refined to the more desirable, lower boiling, gasoline or
fuel oil fractions. High severity cracking has also been practiced for the
conversion of such feedstocks to light, normally gaseous hydrocarbons,
such as ethane, propane or butane.
The present invention relates to the improvement of catalyst performance in
hydrocarbon conversion where metal poisoning occurs. Although referred to
as "metals", these catalystic contaminants may be present in the
hydrocarbon feed in the form of free metals or relatively non-volatile
metal compounds. It is, therefore, to be understood that the term "metal"
as used herein refers to either form. Various petroleum stocks have been
known to contain at least traces of many metals. For example, Middle
Eastern crudes contain relatively high amounts of several metal
components, while Venezuelan crudes are noteworthy for their vanadium
content and are relatively low in other contaminating metals such as
nickel. In addition to metals naturally present in petroleum stocks,
including some iron, petroleum stocks also have a tendency to pick up
tramp iron from transportation, storage and processing equipment. Most of
these metals, when present in a stock, deposit in a relatively
non-volatile form on the catalyst during the conversion processes so that
regeneration of the catalyst to remove deposited coke does not also remove
these contaminants. With the increased importance of gasoline in the world
today and the shortages of crude oils and increased prices, it is becoming
more and more important to process any type or portion of the crude,
including the highly metal contaminated crudes to more valuable products.
Typical crudes which are contaminated with metals and some average amounts
of metal are: North Slope, 11 ppm nickel, 33 ppm vanadium; Lagomedio
(Venezuelan), 12 ppm nickel, 116 ppm vanadium; light Iranian, 16 ppm
nickel, 44 ppm vanadium; heavy Iranian, 30 ppm nickel, 22 pp[m vanadium.
In general, a crude oil can contain from about 5 to 500 ppm nickel and
from about 5 to 1500 ppm vanadium. Moreover, since the metals tend to
remain behind during processing, the bottoms of typical feeds will have an
amount of metals two, three, four times or more than the original crude.
For example, reduced crude or residual stocks can have vanadium levels as
high as 1000-2000 ppm. Typical residual stocks and their vanadium level
include: Sag River atmospheric residuum, 48 ppm vanadium; heavy Iranian
atmospheric residuum, 289 ppm vanadium; Canadian tar sand bitumen, 299 ppm
vanadium; Ti Juana Vacuum residuum, 570 ppm vanadium; Bachaquero Vacuum
residuum, 754 ppm vanadium; and Orinoco Heavy Crude, 1200 ppm vanadium.
The higher the metal level in the feed, the more quickly a given catalyst
will be poisoned and consequently the more often or more effective the
demetallization of that catalyst must be.
Of the various metals which are to be found in representative hydrocarbon
feedstocks some, like the alkali metals, only deactivate the catalyst
without changing the product distribution; therefore, they might be
considered true poisons. Others such as iron, nickel, vanadium and copper
markedly alter the selectivity and activity of cracking reactions if
allowed to accumulate on the catalyst and, since they affect process
performance, are also referred to as "poisons". A poisoned catalyst with
these metals generally produces a higher yield of coke and hydrogen at the
expense of desired products, such as gasoline and butanes. For instance,
U.S. Pat. No. 3,147,228 reports that it has been shown that the yield of
butanes, butylenes and gasoline, based on converting 60 volume percent of
cracking feed to lighter materials and coke dropped from 58.5 to 49.6
volume percent when the amount of nickel on the catalyst increased from 55
ppm to 645 ppm and the amount of vanadium increased from 145 ppm to 1480
ppm in a fluid catalytic cracking of a feedstock containing some metal
contaminated stocks. Since many cracking units are limited by coke burning
or gas handling facilities, increased coke or gas yields require a
reduction in conversion of throughput to stay within the unit capacity.
An alternative to letting catalyst metals level increase and activity and
desired selectivity decrease is to diminish the overall metal content on
the catalyst by raising catalyst replacement rates. Either approach,
letting metals level increase, or increasing catalyst replacement rates,
must be balanced against product value and operating costs to determine
the most economic way to operating. The optimum metal level at which to
operate any cracking unit will be a function of many factors including
feedstock metal content, type and cost of catalyst, overall refinery
balance, etc., and can be determined by a comprehensive study of the
refinery's operations. With the high cost of both catalyst and the
hydrocarbon feedstock today, it is increasingly disadvantageous to discard
catalyst or convert hydrocarbon feedstocks to coke or gas.
Many patents have issued discussing various approaches to removing metals
from hydrocarbon conversion catalysts and then returning the catalyst to
hydrocarbon conversion service. See, for example, U.S. Pat. Nos.
3,150,103; 3,150,104; 3,122,510; 3,173,882; 3,147,228; 3,219,586;
3,182,025; 3,252,918; 4,101,444; 4,163,709; 4,163,710; 4,243,550; and
4,686,197.
As disclosed in U.S. Pat. Nos. 4,686,197, and 4,243,550, both of which are
incorporated herein by reference, a typical treatment of a metal poisoned
catalyst includes regeneration in which portions of the catalyst are
periodically contacted with free oxygen containing gas to removal at least
a portion of the carbonaceous deposits, sulfiding in which the regenerated
catalyst is contacted with sulfiding agents, e.g. H.sub.2 S, to convert
the metals into metal-sulphur compounds to produce a sulfided catalyst,
and chlorination in which the sulfided catalyst is contacted with a
chlorine containing compound to convert the metal poisons to metal
chlorides which can be removed by volatilization and/or aqueous washing.
The catalysts can also be subjected to other processes such as oxidation,
reductive washes, oxidative washes, etc., all of which are aimed at
effecting some removal of the metal poisons.
Sulfiding of the poisoned catalysts is known to be highly advantageous for
nickel removal but less so for the removal of vanadium. For example, it is
known that greater than 80 percent of the nickel can be removed using
conventional, prior are demetallization processes but the removal of
vanadium is significantly less.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved process
for the demetallization of catalysts used for the chemical conversion of
hydrocarbons.
Another object of the present invention is to provide an improved method of
removing vanadium metal from catalysts used for chemical conversion of
hydrocarbons.
Still another object of the present invention to is to provide an improved
method of sulfiding catalysts used for the chemical conversion of
hydrocarbons to enhance vanadium removal.
The above and other objects of the present invention will become apparent
from the description given herein and the appended claims.
The present invention provides an improvement in the demetallization of
catalysts used for the chemical conversion of hydrocarbons wherein a metal
contaminated catalyst containing vanadium is subjected to a sulfiding step
wherein a sulfiding agent such as H.sub.2 S is contacted with the catalyst
at elevated temperatures to convert the metal poisons to metal-sulphur
compounds and the catalyst to a sulfided catalyst. In the improved process
of the present invention, a hydrocarbon having a boiling point of at least
about 300.degree. F. and being at least partially vaporizable at the
sulfiding temperature is introduced into the sulfiding zone together with
the sulfiding agent, the amount of hydrocarbon introduced being sufficient
to enhance vanadium removal of the catalyst being treated. The improved
process leads to enhanced vanadium removal in subsequent downstream
processing of the catalyst. For example, it is common following the
sulfiding step to subject the sulfided catalyst to a chlorination step and
convert the metal-sulphur compounds to metal chlorides which can be more
easily volatilized or removed by various washing techniques well known to
those skilled in the art.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The process of the present invention can be used to demetallize catalysts
used for catalytically promoted methods for the chemical conversion of
hydrocarbons such as cracking, hydrocracking, reforming, hydroforming,
etc. Such reactions generally are performed at elevated temperatures, for
example, about 300.degree. to about 1200.degree. F., more often
600.degree. to 1000.degree. F. Feed stocks to these processes comprises
normally liquid and solid hydrocarbons which at the temperature of the
conversion reaction are generally in the fluid, i.e., liquid or vapor
state and the products and the conversion frequently are lower boiling
materials.
The catalysts which can be treated according to the process of the present
invention may vary widely depending on the use to which the catalyst is
put. In general, any catalyst useful in conversion or cracking of
hydrocarbons in typical hydrocarbon conversion or cracking conditions can
be treated according to the process of the present invention. Typical
conventional catalysts which can be treated according to the process of
the present invention comprises alumina, silica and/or silica-alumina,
silica-magnesia, silica-zirconia, etc. Wholly or partially synthetic gel
catalysts can be treated according to the process of the present
invention, such catalysts generally containing from about 10 to about 30
or event up to 60 percent or more alumina. The catalysts may be only
partially of synthetic material; for example, it may be made by the
precipitation of silica-alumina and clay, such as kaolinite or halloysite.
Other synthetic gel containing cracking catalysts which can be treated
contain alumina added to a natural or synthetic silica-alumina base. The
invention is particularly applicable to catalysts used for hydrocarbon
conversion processes and which contain at least one synthetic crystalline
material in an amount effective to promote the desired hydrocarbon
conversion under hydrocarbon conversion conditions. Materials known as
zeolites or molecular sieves are one preferred class of such synthetic
crystalline materials. Useful zeolites include not only synthetic
zeolites, but also natural occurring zeolites, the chemical makeup of
which is modified or changed to enhance one or more of the catalystic
properties of the naturally occurring zeolite.
Where the desired hydrocarbon conversion involves one or more of
hydrocarbon cracking (preferably in the substantial absence of added free
molecular hydrogen), disproportionation, isomerization, hydrocracking,
reforming, dehydrocyclization, polymerization, alkylation, and
dealkylation, synthetic crystalline materials, alumina silicates, SAPO,
TAPO, MeAPO, AlPO, ZSM-Series, LZ-Z10, LZ-10, USY and the like may be
employed. Certain of these synthetic crystalline materials are discussed
in U.S. Pat. Nos. 4,310,440; 4,440,871; 4,500,651; 4,503,023; and
4,686,197, all of which are incorporated herein by reference.
As disclosed in U.S. Pat. No. 4,686,197 (the '197 Patent), sulfiding of the
catalyst is generally performed after the catalyst has been regenerated or
calcined to remove carbon deposits and, optionally, treatment of the
regenerated catalyst with a molecular oxygen containing gas to increase
vanadium removal. Typically, as pointed out in the '197 Patent, the
regeneration and treatment of the regenerated catalyst with a molecular
oxygen containing gas provides enhanced vanadium removal if those steps
are performed before chlorination of the catalyst.
In conducing the sulfiding, the catalyst is contacted with at least one
sulfiding agent in a sulfiding zone operated at an elevated temperature.
Suitable sulfiding agents include elemental sulfur vapors or more
conveniently volatile sulfides such as H.sub.2 S, CS.sub.2, mercaptans,
etc., H.sub.2 S being a preferred sulfiding agent. The contact with the
sulfiding agent can be performed at an elevated temperature, generally in
the range of from about 500.degree. F. to about 1650.degree. F.,
preferably about 800.degree. F. to about 1500.degree. F. Other sulfiding
conditions can include a partial pressure of the sulfiding agent of about
0.1 to about 30 atmospheres or more, preferably about 0.5 to about 25
atmospheres. Partial pressures of the sulfiding agent below atmosphere can
be obtained either by using a partial vacuum or by diluting the sulfiding
vapor with an inert gas such as nitrogen or hydrogen. The time of contact
of the sulfiding agent with the catalyst may vary widely on the basis of
the temperature and pressure chosen and other factors such as the amount
of metal to be removed, type of catalyst, etc. The sulfiding step may run,
for instance, from about 5 or 10 minutes up to about 20 hours or more
depending on the sulfiding conditions and the severity of the catalyst
poisoning. Pressures approximating 1 atmosphere or less are preferred in
the sulfiding zone with a treatment time of from about at least 1 to about
2 hours, the time of course depending upon the manner of contacting of the
catalyst, the sulfiding agent and the nature of the sulfiding step, i.e.
batch or continuous, as well as the rate of diffusion within the catalyst.
In the sulfiding step, as well known from the prior art, metals are
converted to metal sulfur containing compounds, e.g. vanadium sulfur
containing compounds which are more easily converted to the chloride form
in subsequent chlorination.
Generally speaking, the sulfiding agent is introduced in an inert carrier
gas such as nitrogen, argon, etc., the carrier gas being introduced in an
amount sufficient to provide a fluidized bed within the sulfider.
In the improved process of the present invention, at least one hydrocarbon
is introduced into the sulfiding zone together with the sulfiding agent.
The hydrocarbon employed will have a minimum boiling point of about
300.degree. F., preferably about 330.degree. F., and will be at least
partially vaporizable at the temperature employed in the sulfiding zone.
Preferably, all of the hydrocarbon introduced into the sulfiding zone is
vaporizable at the temperature in the sulfiding zone. While a pure
hydrocarbon having the properties described above can be used, it is more
convenient to introduce a mixture of hydrocarbons wherein at least some of
the hydrocarbons in the mixture has the minimum boiling point of about
300.degree. F. and are vaporizable at the temperature in the sulfiding
zone. In particular, when a mixture of hydrocarbons is employed, it is
preferred that the mixture have a boiling range of from about 300.degree.
F. to about 1000.degree. F., preferably from about 330.degree. F. to about
800.degree. F. Suitable, non-limiting examples of hydrocarbons that can be
employed include pure hydrocarbons such as decane, hendecane, dodecane,
tridecane, tetradecane, oxdecane, eicosane, etc. In cases where the pure
hydrocarbon is a solid at room temperature, it can be conveniently
dissolved in a suitable hydrocarbon solvent and the solution introduced
into the sulfider. Thus, for example, solutions of eicosane and decane can
be conveniently employed. In addition to aliphatic hydrocarbons such as
the alkanes mentioned above, aromatic hydrocarbons possessing the
necessary properties described above for the hydrocarbons and which will
not deleteriously effect the catalyst or undergo undesirable side
reactions can also be employed. Non-limiting examples of suitable
hydrocarbon mixtures include kerosine, diesel oil, gas oil, crude oil,
vacuum distillates, heavy naphtha, etc. Especially preferred as a suitable
hydrocarbon for introduction into the sulfiding zone is diesel oil which
is relatively inexpensive and readily available.
The amount of hydrocarbon introduced into the sulfiding zone will generally
be in an amount of at least about 0.3 percent by weight based on the total
weight of the catalyst charged to the sulfider or sulfiding zone. More
generally, the amount of hydrocarbon introduced into the sulfider will be
in an amount of least about 0.3 up to about 5 percent by weight based on
the weight of the catalyst being treated. While greater amounts of
hydrocarbon can be introduced, generally no enhanced results are observed.
As noted above, it is common in catalyst demetallization processes to
conduct both a sulfiding and a chlorinating step, the chlorinating step
being designed to convert the metal-sulfur compounds into metallic
chlorides which can be more easily removed from the catalyst than the
corresponding metal-sulfur compounds, such removal being conventiently
carried out by vaporization of the metallic chlorides and/or washing of
the catalyst containing the metallic chlorides with suitable aqueous
washes. Such a chlorination step is disclosed in U.S. Pat. No. 4,686,197,
and is incorporated herein by reference.
The present invention is particularly suitable for demetallizing catalysts
utilized in the catalytic cracking of reduced, or topped crude oils to
more valuable products such as illustrated in U.S. Pats. Nos. 3,092,568
and 3,164,542, both of which are incorporated herein by reference.
Similarly, the process of the present invention is applicable to the
treatment of catalysts used to process shale oils, tar sands oils, coal
oils and the like, where metal contamination of the cracking catalysts can
occur.
To more fully illustrate the present invention, the following non-limiting
examples are presented. In the examples which follow, all runs were
conducted in a semi-commercial continuous flow demetallization unit
comprising a cascaded arrangement of a calciner vessel, a sulfider vessel
and a chlorination vessel. The catalyst was subjected to regeneration in
the calciner to remove carbon deposits and heat the poisoned catalyst to
the desired temperature for introduction into the sulfiding zone after
which it was allowed to flow by gravity into the sulfider and then flow by
gravity into the chlorinater. Flow rates of sulfiding agent and inert gas
in the sulfider were sufficent to maintain fludized bed conditions. The
catalyst was analyzed before being introduced into the demetallization
process and after being treated in the demetallization process to
determine the extent of vanadium removal. In all of the examples which
follow, the following conditions were employed:
Catalyst Rate--10 tons per day (TPD)
Calciner Temperature--1400.degree. F.
Chlorinator Temperature--650.degree. F.
H.sub.2 S Flow Rate to Sulfider--500 pounds per day
N.sub.2 Flow Rate to Sulfider--600 pounds per day
Cl1 Flow Rate to Chlorinator--750 pounds per day
Sulfider Pressure--Atmospheric
In all examples which follow, flow rates of of hydrogen sulfide,
hydrocarbon and catalyst were maintained substantially constant. Diesel
oil was used as the hydrocarbon in all cases.
EXAMPLE 1
In this example, the temperature in the sulfiding zone was maintained at
1450.degree. F. Table 1 below shows the percent of vanadium and nickel
removal for two differing feed rates of diesel as well as a comparative
run with no added deisel.
TABLE 1
______________________________________
Deisel Oil Feed
% Nickel Removal
% Vanadium Removal
______________________________________
0 85 30
5 gallons/day (gpd)
85 37
(40 lb/day)
10 gpd 86 45
(80 lb/day)
______________________________________
EXAMPLE 2
The procedure of Example 1 was followed with the exception that the
sulfider temperature was maintained at 1400.degree. F. The results showing
nickel and vanadium removal are shown in Table 2 below.
TABLE 2
______________________________________
Deisel Oil Feed
% Nickel Removal
% Vanadium Removal
______________________________________
0 75 17
5 gallons/day (gpd)
76 23
(40 lb/day)
10 gpd 77 27
(80 lb/day)
15 gpd 77 27
(120 lb/day)
______________________________________
As can be seen from the data above, the use of less than about 0.2 percent
hydrocarbon (diesel oil) based on the total weight of catalyst charged
produces no apparent improvement in vanadium removal. On the other hand,
the use of an amount of hydrocarbon in excess of about 4 percent by weight
based on the total weight of catalyst charged gives no apparent increased
benefit. Accordingly, although amounts in excess of 4 percent of
hydrocarbon based on the weight of catalyst can be employed without any
deleterious effects, economics would dictate that an amount of from about
0.2 to about 5 percent by weight based on the weight of the catalyst
charged be employed.
The foregoing description of the invention has been directed in primary
part to a particular preferred embodiment in accordance with the
requirements of the patent statutes and for purposes of explanation and
illustration. It will be apparent, however, to those skilled in the art
that many modifications and changes in the specifically described
invention may be made without departing from the true scope and spirit of
the invention. Therefore, the invention is not restricted to the preferred
embodiments described, but covers all modifications which may fall within
the scope of the following claims.
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